The characteristics of a given type of rope determine whether that type of rope is suitable for a specific intended use. Rope characteristics include breaking strength, elongation, flexibility, weight, bending fatigue resistance and surface characteristics such as abrasion resistance and coefficient of friction. The intended use of a rope will determine the acceptable range for each characteristic of the rope. The term “failure” as applied to rope will be used herein to refer to a rope being subjected to conditions beyond the acceptable range associated with at least one rope characteristic.
The present invention relates to ropes that are commonly referred to in the industry as “lift lines”. Lift lines are used to deploy (lower) or lift (raise) submersible equipment used for deep water exploration. Bending fatigue and abrasion resistance characteristics are highly important in the context of lift lines.
In particular, a length of lift line is connected at a first end to an on-board winch or capstan and at a second end to the submersible equipment. Between the winch and the submersible equipment, the lift line passes over or is wrapped around one or more intermediate structural members such as a closed chock, roller chock, bollard or bit, staple, bullnose, cleat, a heave compensating device, or a constant tensioning device.
When loads are applied to the lifting line, the lifting line wraps around such intermediate structural members and is thus subjected to bending fatigue and abrasion at the intermediate structural members. Abrasion and heat generated by friction at the point of contact between the lifting line and the intermediate structural members can create wear on the lifting line that can affect the performance of the lifting line and possibly lead to failure thereof.
The need thus exists for improved ropes for use as lifting lines that have improved bending fatigue and abrasion resistance characteristics.